Drilling fluids are used in drilling deep wells, such as wells for extraction of oil or natural gas. The drilling fluids help to keep the well bore open and also flush cuttings made by the drill bit to the surface. In a typical drilling operation, drilling fluid (also called drilling mud) is pumped down through the bore of a drill string to a drill bit. The drilling fluid exits through apertures in the drill bit and returns to the surface in an annular space between the drill string and a wall of the drill bore. The drilling fluid carries with it cuttings of rock or other material that is being drilled through.
At the surface, the cuttings are separated from the drilling fluid so that the drilling fluid may be reused. This separation may occur in several stages. In a typical operation, the drilling fluid is first passed through a shale shaker. The shale shaker comprises a vibrating screen. Large cuttings do not pass through the screen whereas the drilling fluid and small particles pass through the screen. The drilling fluid is then typically passed through a centrifuge. In most cases the centrifuge is a horizontal decanter-type centrifuge. The centrifuge separates smaller particulate solids from the drilling fluid. The drilling fluid is then returned to a tank from which it can be reused.
Various types of drilling fluid are used. Oil-based drilling fluids are used in some circumstances. Such oil-based drilling fluids have properties that are desirable in some applications. One difficulty that occurs, particularly with oil-based drilling fluids, is that the separation of particles from the drilling fluid is not perfect. Particles that have been separated by a shale shaker or a centrifuge typically carry some drilling fluid with them. Oily materials can constitute environmental hazards. In most jurisdictions it is not legal to dump cuttings or other soil which is contaminated with oil. Thus, disposing of cuttings in cases where an oil-based drilling fluid has been used can be very expensive.
In some cases, the oil content of the cuttings is sufficiently high that regulations govern the transportation of the cuttings. Such regulations can require that the cuttings be mixed with sawdust or another oil-absorbent material to prevent the release of oil during shipment. This adds significantly to the expense of transportation and also increases the volume of material to be disposed of, thus compounding a problem.
It is common practice to truck cuttings to a storage area and to store the cuttings until such time as somebody finds a practical way to remediate the cuttings by removing or breaking down the oil which coats the particles of the cuttings. The existence of such storage areas is a significant potential liability.
Various methods for removing oils from soil or other similar materials have been proposed in the literature. Some such methods are economically impractical and others do not work.
There is a need for cost-effective, practical methods and apparatus able to remove oils from soils and other similar materials. There is a particular need for such methods and apparatus that are suitable for alleviating the problems described above.